My dissertation, The Planet as Self-Regulating System: Configuring the Biosphere as an Object of Knowledge, 1940–1990, examines the emergence and historical trajectory of the biosphere in the American postwar biological and environmental sciences. First theorized in the early twentieth century, but introduced to American scientific communities in the immediate postwar years, the biosphere concept dissolves the boundary between organisms and environments to construe the whole of planetary nature in terms of chemical cycles and flows. Drawing on a range of archival sources, my project tracks how the concept came to be constituted as an object of inquiry across a wide variety of disciplines over the course of the second half of the twentieth century. This interdisciplinary approach to the history of the biosphere reveals that the meaning of the concept has historically been flexible and multiple, linked to historical genealogies as diverse as the political economy of natural resource extraction, cybernetics and general systems theory, ecotoxicology, and the search for extraterrestrial life.